docs: def _execute_callback(self, status, message, job, res, err, stacktrace):
          """Execute the callback.
  
          :param status: Job status. Possible values are "invalid" (job could not
              be deserialized or was malformed), "failure" (job raised an error),
              "timeout" (job timed out), or "success" (job finished successfully
              and returned a result).
          :type status: str
          :param message: Kafka message.
          :type message: :doc:`kq.Message <message>`
          :param job: Job object, or None if **status** was "invalid".
          :type job: kq.Job
          :param res: Job result, or None if an exception was raised.
          :type res: object | None
          :param err: Exception raised by job, or None if there was none.
          :type err: Exception | None
          :param stacktrace: Exception traceback, or None if there was none.
          :type stacktrace: str | None
          """
          if self._callback is not None:
              try:
                  self._logger.info('Executing callback ...')
                  self._callback(status, message, job, res, err, stacktrace)
              except Exception as e:
                  self._logger.exception(
                      'Callback raised an exception: {}'.format(e))